The proposal requests support for prospective continuation of a population-based cross-sectional study of insulin secretory reserve and glucose tolerance among the adults of Wadena, MN. The target subjects include 60 previously-diagnosed diabetic individuals, and 400 members of a random sample of adults without previously-known diabetes, chosen from a 99%-complete census of adult residents, stratified for age, gender, and use or non-use of chronic medication. C-peptide in a 4-hour timed urine collection, and plasma C-peptide, will be measured following a 75 gm oral glucose load, as part of a glucose tolerance test (National Diabetes Data Group methodology); these tests will be performed 3 and 6 years after the initial cross-section study. The study will test these central hypotheses: 1) most non-insulin-dependent diabetic (NIDDM) subjects show generous insulin production, sustained overtime; 2) older non-diabetic subjects show no systematic decline in insulin production; 3) a small subset of NIDDM subjects, identiable by immunologic tests, are at risk for declining insulin production and represent a different disorder; 4) risk for vascular complications (eye, kidney, heart) is related to degree of hyperglycemia rather than type of diabetes. The results should have value in guiding future studies of the nature of the common form of diabetes and in eventual development of more rational treatments than is currently available. The study is a cooperative project among treatment than is currently available. The study is a cooperative project among the schools of Medicine and Public Health, University of Minnesota, Minnesota Department of Health, and the Wadena Medical Center and Tri- county Hospital.